High speed drafting process



S S E c m JP m L n EM FR HIGH SPEED D of 2 FIG. IB

Sheet FIG. 28

FIG. 2A

INVENTQR FRE DERICK C. FIELD, JR.

ATTORNEY April 15, 1969 F. c. FIELD, JR 3,438,094

HIGH SPEED DRAFTING PROCESS Filed Sept. 2, 1966 Sheet 3 of 2 FIG. 3A FIG. 3B

ZNVEN'TOR FREDERICK C. FIELD, 7 JR.

ATTORNEY United States Patent 3,438,094 HIGH SPEED DRAFTING PROCESS Frederick C. Field, In, Wilmington, Del., assignor to E. L du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Sept. 2, 1966, Ser. No. 576,973 Int. Cl. Dlllh 5/72 US. Cl. 19-288 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to improved technology for conveying textile fibers and more particularly to an improved drafting apparatus and process for textile staple fibers.

In attempting to increase the speeds of commercial fiber drafting, it has been found that the uniformity of drafting is impeded by excessive air turbulence, static, and other causes created by the high speed set of front rolls in the drafting system. Some staple fibers are blown away from the nip and tend to shunt around the rolls or enter the nip in a disoriented manner. This effect becomes more pronounced as the speed of the front rolls is increased and when the denier per filament of the fiber is reduced and when the number of fibers delivered is reduced to give a finer yarn. Some attempts have been made to design modified drafting systems for alleviating these problems but these have not resulted in sufliciently better uniformity of drafted sliver, lower nep count, and lower incidence of spinning discontinuities at the more elevated speeds. It is desirable to prevent fiber ends from diverging from the bundle at the exit of the nip to an extent that could cause fibers to wrap on the front roll.

An object of this invention is to provide an improved process and apparatus for handling textile staple fibers. Another object is to design a combined drafting system to permit the drafting of staple fibers to avoid fiber ends separating from the main fiber bundle because of air turbulence or excessive static forces as they approach, pass through and leave the nip of the front set of rolls. A further object is to provide a combined apertured front roll together with an aspirating means immediately following the roll for conveying staple fibers at high speeds to produce more uniform yarns having less fuzz and fewer imperfections. Other objects will be apparent from a description of the invention given below.

These and other objects are accomplished by providing a staple fiber conveying system for preparing yarn by twist transference comprising a pair of rolls in nip relationship to grip and advance the fiber where at least one of said rolls has surface apertures with an internal pas sage connecting the apertures to allow a continuous fluid flow through the passage from one side of the nip to the other side, and means for maintaining a pressure reduction immediately after the nip as compared to the pressure at the nip entrance to provide fluid flow in the same direction as the fiber movement. Preferably, the invention provides an improved drafting system having the conventional pair of back rolls for metering the sliver and a pair of front rolls operating at a higher speed than the back rolls and one of which contains said apertures, where- 3,438,094. Patented Apr. 15, 1969 in a differential air pressure is applied across the nip of the two front rolls, the higher pressure being on the inlet side of the nip.

The invention also includes an improvement to the process of staple fiber drafting by passing a sliver between at least two pair of rolls and rotating the exit pair of rolls at a higher speed than the preceding rolls. The improvement comprises reducing the pressure immediately after the exit rolls, channelling the fluid medium surrounding the sliver in the nip of the exit rolls towards the zone of reduced pressure through one of the exit rolls and removing drafted sliver and fluid from the reduced pressure zone. When the improved apparatus is used for drafting sliver, a pair of high speed cooperating nip rolls are used wherein at least one of said rolls is composed of an essentially solid core and containing apertures in the roll surface and around the circumference of the roll, the apertures being of such size and spacing that a compressing pressure is maintained on the fibers passing through the nip while allowing escape of cocurrent fluid through the apertures along the line of travel of the sliver. The cocurrent flow of fibers and fluid may enter the nip rolls in a generally horizontal path or in a generally vertical path. When an apertured roll is employed for allowing escape of air, such a roll may be used with a solid surface roll, or two apertured rolls may be used to form the nip. Obviously, different patterns may be employed to design the apertures in the roll, which for most drafting applications will be employed as the front bottom roll. Two basically different types of apertured rolls may be used in this invention; one in which the apertures may be cut across the roll axis as slots in the surface of the roll and extend into the roll or in the other case, the apertures may be cut partially in the surface of the roll combined with an undercut immediately adjacent the roll surface but below the surface apertures. Regardless of the particular design of apertured roll, the passage of the air or other fluid remains cocurrent with the passage of the fibers being drafted in the nip, except for temporary and instantaneous deflection of the air passage through the surface apertures of the roll, and then the air returns in association with the fibers at the exit end of the nip and continues in cocurrent relationship with the fibers. This cocurrent passage of air and fibers through the nip is governed not only by the design of the apertures in at least one of the nip rolls, but also because of the location of a pressure reducing means (e.g. vacuum or aspirating force) downstream of the exit at the nip of the rolls.

A number of different designs for an apertured roll for use in this invention will be readily apparent to those skilled in the art.

FIGURES 1A, 1B, 2A, 213, 3A and 3B represent front and side views of several forms of apertured rolls employed in this invention.

The other features and operation of the invention are illustrated in the following drawings wherein:

FIGURE 4 is a schematic view of a drafting system in accordance with this invention illustrating the combination of apertured bottom front roll and an external aspirating means beyond the nip of the front rolls.

The present invention combines the apertured nip rolls and the pressure reduction (aspirating means) external of the nip rolls and positioned at the exit of the nip of the front rolls and directly in line with the passage of fibers through the nip. By designing an essentially solid bottom or blocked end front roll, it has been possible to retain the simple line shaft construction characteristics of conventional drafting systems and to achieve a high level of position-to-position uniformity at elevated speeds upward of 300 yards per minute. Also critical in the operation of this invention is the arrangement whereby the air is caused to follow in a path substantially cocurrently with the direction of fiber travel into the nip of the front rolls, so that the air exiting from the area of the nip is allowed to lift any stray fibers or fiber ends from the surface of the front rolls and thereby prevent fibers from wrapping around the front roll. The amount of air flow is not critical as long as the turbulent air is removed from the nip entrance. The amount of air flow required, as controlled by pressure differential across the nip, can be easily adjusted by the operator for a particular drafting speed.

FIGURE 4 illustrates schematically the general arrangement of elements in a suitable sliver drafting system containing three pairs of drafting rolls which can give a draft of about to 3000 or more. In addition to the necessary draft rolls, the drafting system of this invention may include other conventional modifications. For example, drafting control aprons 34, 35, 45 and 46 may be used as shown in FIGURE 4, passing over rolls 36, 37, 47 and 48, respectively, such that these control aprons are located as close to the nips of the draft rolls as is practical to provide an even delivery of fibers to the nips. In conventional drafting systems, it is customary to use only two pairs of drafting rolls. The present invention is applicable to all drafting systems and is not dependent on the herein described apparatus of FIGURE 4. When drafting systems comprising two pairs of drafting rolls are utilized a draft of 10 to 400 or greater can be accomplished. Normally, the front draft rolls are made of steel cores with the top roll having a surface covered with conventional hard rubber/cork composition, and the bottom roll 31 having a surface of steel. FIGURE 4 also illustrates the critical positioning of the aspirating means 41 adjacent the nip of the front rolls and externally thereof at the exit end of the nip in order to aspirate air and drafted fibers cocurrently from the exit area of the nip through the aspirating means, and to forward the drafted fiber bundle to a guide twister 42. A suitable twister is disclosed in FIGURE 4 of US. Patent 3,079,746 to Field. The aspirating means is preferably positioned within the contour of said exit roll.

One suitable form of apertured bottom front roll 31 is illustrated in FIGURE 4 which provides for an air stream to enter the surface apertures of this roll and pass through undercut channel 60 which is in a complete circle concentric with the outside circumference of the roll providing a path for the air continuously in any and all positions of rotation of roll 31. Following the illustration in FIGURE 4, the air flows to channel 60 from the area immediately before the nip, exits from the channel through other apertures immediately after the nip and then passes through the mouth of aspirating jet 41. At the same time that the aspirated air follows the path just described, the fiber raw material is presented by aprons 45 and 46 and positively conveyed to the nip of the front rolls. The reduced pressure from aspirator 41 at the exit side of the nip provides a force to not only pull air through the nip but also any loose or stray staple fibers or ends on the surfaces of rolls 30 and 31 after exit from nip 40, which are not part of the drafted fiber bundle, are picked up by the air stream as it is pulled into the aspirating jet 41.

As is evident from the different patterns of apertures illustrated in the various views of FIGURES 1, 2 and 3, the exact pattern of the apertures on the novel front bottom roll 31 is not important by itself. The crictical feature of the apertures in the front roll 31 for use in this invention is that they be of a size, shape and frequency positioned all the way around the circumference of the roll such that both the drafting force on the fibers remains constant and that the fluid surrounding the fibers in the nip entrance be continuously and cocurrently passed to the nip exit. Two entirely different modifications of apertured front rolls are illustrated as suitable herein. One modification is such that the apertures 11 cross the roll axis and are cut into the surface of roll 31 and do not extend in the form of a complete circumferential surface undercut for the roll, which is illustrated in FIG- URES 1A and 1B. Each out forms its own surface aperture and internal passage. The second roll form can be considered as a cage which is shown in FIGURES 2A and 2B and provides apertures 12 in the surface of the roll 31 for entrance and exit of aspirating air near the nip. In addition, an undercut channel is placed beneath the surface of the roll in order to provide for passage of the air close to the nip entrance of the front rolls at the instantaneous times When the air reaching the surface of the bottom front roll is interrupted by the nonperforated surface portions of said roll. This provides for complete dissipation of any turbulence that may tend to build up at the entrance side of the nip because of very high speed operation of the front rolls. A reinforcing rib 13 is used to prevent the roll surface from collapsing. A third type roll is illustrated in FIGURE 3 where circumferential grooves 14 are cut into the roll 31 and then the outer roll wall is intermittently replaced by supports 15 across the grooves which result in a net effect similar to roll 31 of FIGURE 2.

The invention i illustrated by the following examples.

Example I A drafting system is used for drafting 140 grains per yard (88,000 den.) sliver composed of 1.5 d.p.f. discontinuous polyacrylonitrile fiber. The drafting apparatus comprised back rolls, middle rolls and front rolls. The bottom front roll was provided with suitable apertures by milling grooves, each 0.0156 inch (0.396 cm.) wide, 0.0312 inch (0.0793 cm.) center to center, 0.090 inch (0.228 cm.) deep, 0.80 inch (2.03 cm.) long, distributed at 15 intervals around the surface of a stainless steel roll. The top front roll was provided with a smooth surface of conventional hard rubber/cork composition. This design of apertured bottom front roll makes it possible to pull sufficient air through the nip of the two front rolls using an aspirating jet at the exit side of the nip so as to entrain the fibers through the nip that otherwise are shunted around the rolls or passed through the nip in a disoriented fashion. This drafting system was operated with the back rolls at .42 yard per minute (.38 meter), middle rolls at 6.3 yards per minute (5.7 meters), and the front rolls at a surface speed of 416 yards per minute (380 meters), without any deviation of staple fibers from their intended path, to produce a 60 cotton count yarn (88 denier) with a high degree of evenness.

Example II An grain per yard (about 51,000 denier) sliver composed of 3.0 denier per filament discontinuous polyamide fiber is drafted on an apparatus having back rolls, middle rolls and front rolls. The bottom front roll is of the cage design of FIGURES 2A and 2B and the top front roll has an outer surface of a rubber/cork composition. The rolls are rotated at the following speeds:

Back rolls About 1 yard per minute. Middle rolls About 15 yards per minute. Front rolls About 217 yards per minute.

This drafting system produced a uniform 25 cotton count yarn (about 212 denier).

Example 111 A 30 grain per yard (about 32,000 denier) sliver composed of 0.7 denier per filament discontinuous polyester fiber is drafted on an apparatus having back rolls, middle rolls and front rolls. The bottom front roll is of the cage design of FIGURES 2A and 2B and the top front roll has an outer surface of a rubber/cork composition. The rolls are rotated at the following speeds:

Back rolls About .53 yard per minute. Middle rolls About 8 yards per minute. Front rolls About 307 yards per minute.

This drafting system produced a uniform 100 cotton count yarn (about 53 denier).

The chief advantage of this invention is to provide modifications to existing fiber conveying systems to permit drafting sliver and spinning yarn at speeds greater (e.g. high as 50 to 100 times greater) than commercially possible up to the present time, without in turn affecting the uniformity of the resulting sliver or yarn. In conventional drafting operations when a pair of drafting rolls are rotated to give roll surface speeds of about 50 to 100 yards per minute, turbulence at the nip entrance causes fiber displacement which results in a poor yarn. In addition, this invention permits the conveying and drafting of staple fibers at high speeds Without fiber ends separated from the main fiber bundle at the exit of the nip and in some cases wrapping around the front roll. A particular advantage of the present invention is based on the fact that the modified high speed fiber handling system is particularly advantageous for producing staple yarns such as those described by Field in US. Patent 3,079,746. The bundle is conveyed through and drafted at the nip between the front rolls in a pneumatic air stream, and as the drafted fibers exit from the nip in the air stream, the force and direction of the cocurrent air lifts from the roll surface beyond the nip particularly the staple fibers which are free of twist and which tend to stray from the main bundle onto the surface of the rolls, and combines these loose fibers together with the rest of the bundle exiting in the air stream through the opening in the aspirating jet. This action of the air stream on the fiber bundles, processed in the above-mentioned Field patent, insures a sufiicient quantity of fibers free of twist to give excellent wrapping of these free fibers around the core fibers to produce the novel spun yarns described and claimed in the specified patent. This lifting action of the air stream to remove stray fibers from the roll surface is quite different from the compacting action of some other methods for drafting staple fibers wherein the negative air pressure acting on the fibers at the nip is at right angles to the cocurrent air and fibers entering the nip.

The present invention is useful for conveying and forwarding of staple textile fibers at high speeds, and particularly for uniformly drafting sliver or roving for making spun yarns or core spun yarns, which in turn are useful for a wide variety of woven, knitted, and nonwoven fabrics in many apparel and industrial textile applications. The staple fibers useful for conveying and drafting at higher speeds in accordance with this invention include not only natural fibers, such as cotton and wool, but also synthetic fibers, such as those made from polyamides, polyesters, acrylic polymers and copolymers, vinyl polymers and copolymers, polyurethanes, olefin polymers and copolymers, cellulose derivatives such as cellulose acetate, regenerated cellulose, and the like. Blends of two or more natural fibers, two or more synthetic fibers, or blends of natural and synthetic fibers may also be drafted according to the improvements provided by this invention.

What is claimed is:

1. A high-speed drafting process for preparing uniform drafted fibers which comprises:

(A) passing discontinuous fibers through at least two pairs of rolls maintained in nip position where the exit rolls rotate at a higher speed than the entrance rolls,

(B) reducing the fluid pressure immediately past the nip of said exit rolls to give a pressure reduction between the fluid surrounding said fibers immediately before and after said exit roll nip,

(C) delivering said fibers at speeds greater than 50 yards per minute from said exit roll nip, and

(D) cocurrently flowing said fluid, in the direction of fiber delivery, through apertures in at least one of said exit rolls as said fibers leave the exit roll nip.

2. A high-speed drafting process as defined in claim 1 where said fiber is passed between two pairs of rolls exerting a draft of 10 to 400.

3. A high-speed drafting process as defined in claim 1 where said fiber is passed between three pairs of rolls exerting a total draft of at least 25.

4. In a process for drafting staple fiber and consolidating said fiber by twist transference the improvement of increasing the uniformity of drafted product for delivery for said twisting which comprises rotating the exit rolls at a speed greater than 50 yards per minute, reducing the fluid pressure at the downstream side of the nip 0f the exit rolls and passing the fluid surrounding said staple fiber on the upstream side of said nip through openings in at least one of said rolls to give unobstructed air passage cocurrently with fiber passage.

References Cited UNITED STATES PATENTS 1,474,346 11/ 1923 Campbell.

3,079,746 3/1963 Field 57-51 3,251,100 5/1966 Ingham 19-263 3,296,664 1/1967 Ingham et a1 19288 DORSEY NEWTON, Primary Examiner. 

